A potential hurdle in developing cell replacement therapies using human embryonic stem cells (hESCs or hES cells) is that differentiation methods may not specify all hESCs homogeneously. Undifferentiated hESCs, partially differentiated or progenitor cells, or incorrectly specified cells may persist within differentiated cell populations. The presence of such cells may contribute to “off-target” biological effects upon implantation, the largest perceived issue being implant overgrowth or generation of teratomas. It is not clear if teratomas are caused solely by persistent hESCs, or if partially differentiated or progenitor cells also contribute to teratoma formation. Regardless, it will be important to demonstrate that transplantable cell populations are safe and do not contain teratoma-causing subpopulations.
It is possible to minimize unwanted subpopulations of cells, or purify desirable populations prior to transplantation or delivery, by depleting, isolating, killing or inhibiting undifferentiated cells using a variety of approaches that involve targeted agents such as small molecule organic compounds, cell surface markers or antibodies (Choo et al. Stem Cells 2008 2:1454-63). There is thus a need to identify agents and methods that can be used to eliminate potentially unsafe populations of otherwise transplantable cells.